Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$63.35	12.449%	$71.2364	$71.24	$71.25	$71.20
Purchase #2	$73.56	6.497%	$78.3392	$78.34	$78.35	$78.30
Purchase #3	$146.28	8.530%	$158.7577	$158.76	$158.75	$158.80
Purchase #4	$76.25	3.814%	$79.1582	$79.16	$79.15	$79.20
Purchase #5	$137.58	3.144%	$141.9055	$141.91	$141.90	$141.90
Purchase #6	$74.71	5.235%	$78.6211	$78.62	$78.60	$78.60
Purchase #7	$85.48	3.674%	$88.6205	$88.62	$88.60	$88.60
7 purchase totals =	$657.21		$696.6386	$696.65	$696.60	$696.60